1. Field of the Invention
The invention relates to a blowout preventer which may be utilized within the hydraulic circuitry extending from a control panel to a safety valve within a subterranean well.
2. Description of the Prior Art
In order to isolate a subterranean oil or gas well during a blowout, fire or other catastrophe, safety valves which may be manipulated between open and closed position by variance of hydraulic pressure contained within a line extending from the safety valve to a control panel at the surface of the well are utilized. Typically, such control systems have utilized an hydraulic-pneumatic interface valve which is sensitive to variance within a pneumatic signal source which detects abnormal well conditions such that the pneumatic signal will activate the interface valve to send hydraulic pressure to the downhole safety valve and maintain the safety valve in open position until an adverse well condition causes sufficient variation within the pneumatic signal source to, in turn, cause the interface valve to shift and vary the hydraulic pressure signal to the safety valve to manipulate it to closed position. As the hydraulic-pneumatic interface valve is activated, the interface assembly shifts to block hydraulic supply and concurrently bleeds pressure out of the control line extending to the downhole safety valve. However, such assemblies having an hydraulic-pneumatic valve within the console permit a continuous communication of fluid within the control line to the reservoir after the shut-in signal has been activated, because the dump port within the hydraulic-pneumatic interface valve is opened and remains opened even though the downhole safety valve has been manipulated to closed position. In the event of a packing, i.e., chevron seal, failure immediate the safety valve assembly, or in the event of a rupture within the control line extending to the well, the open port within the hydraulic-pneumatic interface valve assembly will permit well and control fluids to flow up through the control line and into the reservoir within the control unit. After a period of time the reservoir will overfill, and a resultant potential fire hazard or pollution environment may result. In geographically remote locations, this continuous abnormal control line bleeding might occur for considerable period of time before personnel could be sent to location to correct the deficiency, kill the well, or place the well back on production.
The present safety valve or blowout preventer is needed to remedy this particular problem without adversely affecting normal flow and operation during opening and closing manipulation of the safety valve. Additionally, the present blowout preventer is designed such that there is never adverse interference with control line flow during the opening mode for the downhole safety valve. More importantly, when the safety valve is desired to be closed during normal operations, the closing manipulation of the safety valve is not interfered with by utilization of the control line blowout preventer of the present invention when incorporated in the circuitry. The present blowout preventer is operable such that the safety valve may be repeatedly opened and reopened. Only when excessive flow returns are encountered within the blowout preventer during an abnormal closing of the safety valve, or during emergency shutdown of the well, is the blowout preventer feature of the present apparatus activated such that the control line from the blowout preventer to the safety valve is isolated from the hydraulic circuitry extending from the blowout preventer to the control panel. Additionally, the blowout preventer apparatus of the present invention permits automatic resetting such that the safety valve may be reopened even after excessive fluid volume returns are encountered through the apparatus as a result of returns of fluid in excess of the amount of fluid required to actually displace the safety valve to the closed position, as the result of utilization of a plurality of, for example, chevron seals to control pressure transmission immediate the safety valve.
Although the present invention preferably is utilized on control lines extending to subterranean safety valves or actuators therefor, it must be appreciated that the invention is readily adapted to any fluid transmission line, such as hydrocarbon pipe lines, and the like.